Charles Darwin and Alfred Russel Wallace

On the Tendency of Species to Form Varieties, and on the Perpetuation of Varieties and Species by

Natural Means of Selection1858

Reissued with a Preface and Commentary

By Michael T. Ghiselin

California Academy of Sciences

2008

California Academy of Sciences

San Francisco, California

Copyright © 2008 by the California Academy of Sciences

All rights reserved. No part of this publication may be reproduced or

transmitted in any form or by any means, electronic or mechanical,

including photocopying, recording, or any information storage or

retrieval system, without permission in writing from the publisher.

Charles Darwin and Alfred Russel Wallace

On the Tendency of Species to Form Varieties, and on the Perpetuation of Varieties and Species by

Natural Means of Selection1858

Reissued with a Preface and Commentary

By Michael T. Ghiselin

California Academy of Sciences

PREFACE

The Darwinian revolution is widely considered the most important event in the

entire history of the human intellect. But when did it begin? The revolution that

gave the thirteen American colonies their independence from Great Britain might

be said to have started when organized armed conflict broke out at the battles of

Lexington and Concord in 1775. The decisive break, however, occurred with the

Declaration of Independence on July 4, 1776. By analogy, we might say that

Darwinian revolution began on July 1, 1858, with the reading of a joint communi-

cation by Charles Darwin and Alfred Russel Wallace before the Linnean Society

of London. That was, so to speak, the opening shot. Of course it was the publica-

tion, on November 24, 1859, of Darwin’s book On the Origin of Species by Meansof Natural Selection, or the Preservation of Favoured Races in the Struggle forLife that really got the struggle going. It took about ten years for Darwin and his

followers to convince most of the scientific community that evolution is a fact, and

another hundred or so for natural selection to be generally recognized as the main,

though not exclusive, cause of it. Of course, it was not just a revolution in science

for it affected so many aspects of human life and culture. And it is no exaggera-

tion to say that the Darwinian revolution is still going on.

The joint publication established Darwin and Wallace as co-discoverers of the

principle of natural selection. The circumstances surrounding this event were most

unusual, and the fact that Darwin and Wallace were both happy with the arrange-

ment says a great deal about the character of the two scientists. Darwin’s two parts

are quite different from that of Wallace. The first was an excerpt of a draft of a

book that he had written in 1844. It was intended to show that he had discovered

natural selection many years previously. The second was taken from a letter to Asa

Gray of Harvard University dated September 5, 1857. It was intended to show,

among other things, that although Darwin had not yet published on natural selec-

tion, he had discussed it privately with his colleagues, and that he was in fact writ-

ing a book about it.

3

4

Charles Darwin, ca.1854Alfred Russel Wallace

Asa Gray

Wallace’s contribution reads like a

preliminary note on an idea that had

recently occurred to him. Evidently he

was not sure whether it was ready for

publication, and his reason for sending

it to Darwin was to ask his older, and

much esteemed, colleague what he

thought of it. Nonetheless it provides a

very clear exposition of the principle of

natural selection. Wallace also explains

how his ideas are superior to those of

Lamarck, and how natural selection

might explain adaptation and the diver-

sification of life through time.

The manuscript was read to the

Linnaean Society on July 1, 1858, and

the printed version was distributed in

August of the same year. In retrospect,

we can easily appreciate the impor-

tance of the ideas that it contains. The

original audience and readers were in a

quite different situation than we are.

Many would have found it difficult to

understand, and the larger implications

were not obvious. Both Darwin and

Wallace explain the struggle for exis-

tence that results as a consequence of

competition for limited resources. And

both use the analogy of the artificial

selection, in which breeders of domes-

ticated animals and plants select the

kind of organism they prefer as breed-

ing stock, with natural selection, in

which the conditions of existence have

the same basic effect. Readers of the paper at the time it was published would not

have objected to the proposition that selection, whether artificial or natural, might

produce a limited amount of change, giving rise to breeds and perhaps varieties

within species. Whether selection is sufficient to account for the origin of new

species, let alone the descent of all organisms from a single common ancestor,

5

Charles Lyell

Joseph Dalton Hooker

would obviously have met with much more resistance. So, until the Origin ofSpecies was published, natural selection evoked little more than curiosity upon the

part of the scientific community. People knew that Darwin was writing a book.

They awaited its publication with interest. But they did not anticipate what

Wallace called “a new science,” much less its philosophical implications.

TEXT

On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties

and Species by Natural Means of Selection. By CHARLES DARWIN, Esq., F.R.S.,

F.L.S., & F.G.S., and ALFRED WALLACE, Esq. Communicated by Sir CHARLES

LYELL, F.R.S., F.L.S., and J. D. HOOKER, Esq., M.D., V.P.R.S., F.L.S., &c.

[Read July 1st, 1858.]

London, June 30th, 1858.

MY DEAR SIR,—The accompanying papers, which we have the honour of commu-

nicating to the Linnean Society, and which all relate to the same subject, viz. the

Laws which affect the Production of Varieties, Races, and Species, contain the

results of the investigations of two indefatigable naturalists, Mr. Charles Darwin

and Mr. Alfred Wallace.

These gentlemen having, independently and unknown to one another, con-

ceived the same very ingenious theory to account for the appearance and perpetu-

ation of varieties and of specific forms on our planet, may both fairly claim the

merit of being original thinkers in this important line of inquiry; but neither of

them having published his views, though Mr. Darwin has for many years past been

repeatedly urged by us to do so, and both authors having now unreservedly placed

their papers in our hands, we think it would best promote the interests of science

that a selection from them should be laid before the Linnean Society.

Taken in the order of their dates, they consist of:—

1. Extracts from a M.S. work on Species*, by Mr. Darwin, which was

sketched in 1839, and copied in 1844, when the copy was read by Dr. Hooker, and

its contents afterwards communicated to Sir Charles Lyell.

{1}

The first Part is

devoted to “The Variation of Organic Beings under Domestication and in their

Natural State;” and the second chapter of that Part, from which we propose to read

to the Society the extracts referred to, is headed, “On the Variation of Organic

Beings in a state of Nature; on the Natural Means of Selection; on the Comparison

of Domestic Races and true Species.”

6

* This MS. Work was never intended for publication, and therefore was not written with care.—C.D. 1858.

{1} These dates are inaccurate and misleading. Darwin wrote a rough outline, traditionally called the “Sketch” in 1842

and expanded it into a book called the “Essay” in 1844. (M.T.G.)

2. An abstract of a private letter addressed to Professor Asa Gray, of Boston,

U.S., in October 1857, by Mr. Darwin, in which /45-46/ he repeats his views, and

which shows that these remained unaltered from 1839 to 1857.

{2}

3. An Essay by Mr. Wallace, entitled “On the Tendency of Varieties to depart

indefinitely from the Original Type.” This was written at Ternate in February 1858,

for the perusal of his friend and correspondent Mr. Darwin, and sent to him with

the expressed wish that it should be forwarded to Sir Charles Lyell, if Mr. Darwin

thought it sufficiently novel and interesting. So highly did Mr. Darwin appreciate

the value of the views therein set forth, that he proposed, in a letter to Sir Charles

Lyell, to obtain Mr. Wallace’s consent to allow the Essay to be published as soon

as possible. Of this step we highly approved, provided Mr. Darwin did not with-

hold from the public, as he was strongly inclined to do (in favour of Mr. Wallace),

the memoir which he had himself written on the same subject, and which, as

before stated, one of us had perused in 1844, and the contents of which we had

both of us been privy to for many years. On representing this to Mr. Darwin, he

gave us permission to make what use we thought proper of this memoir, &c.; and

in adopting our present course, of presenting it to the Linnean Society, we have

explained to him that we are not solely considering the relative claims to priority

of himself and his friend, but the interests of science generally; for we feel it to be

desirable that views founded on a wide deduction form facts, and matured by years

of reflection, should constitute at once a goal from which others may start, and

that, while the scientific world is waiting for the appearance of Mr. Darwin’s com-

plete work, some of the leading results of his labours, as well as those of his able

correspondent, should together be laid before the public.

We have the honour to be yours very obediently,

Charles Lyell.

Jos. D. Hooker.

J. J. Bennett, Esq.,Secretary of the Linnean Society.

I. Extract from an unpublished Work on Species, by C. DARWIN, Esq., consisting ofa portion of a Chapter entitled, “On the Variation of Organic Beings in a stateof Nature; on the Natural Means of Selection; on the Comparison of DomesticRaces and true Species.”

De Candolle, in an eloquent passage, has declared that all nature is at war,

one organism with another, or with external nature. /46-47/ Seeing the contented

7

{2} Again this claim is misleading. Although many of Darwin’s ideas go back as far as 1838, the principle of diver-

gence of character was discovered around 1852. (M.T.G.)

face of nature, this may at first well be doubted; but

reflection will inevitably prove it to be true. The war,

however, is not constant, but recurrent in a slight

degree at short periods, and more severely at occa-

sional more distant periods; and hence its effects are

easily overlooked. It is the doctrine of Malthus

applied in most cases with tenfold force. As in every

climate there are seasons, for each of its inhabitants,

of greater and less abundance, so all annually breed;

and the moral restraint which in some small degree

checks the increase of mankind is entirely lost. Even

slow-breeding mankind has doubled in twenty-five

years; and if he could increase his food with greater

ease, he would double in less time. But for animals

without artificial means, the amount of food for each

species must, on an average, be constant, whereas the

increase of all organisms tends to be geometrical, and

in a vast majority of cases at an enormous ratio.

Suppose in a certain spot there are eight pairs of

birds, and that only four pairs of them annually

(including double hatches) rear only four young, and

that these go on rearing their young at the same rate,

then at the end of seven years (a short life, excluding

violent deaths, for any bird) there will be 2048 birds,

instead of the original sixteen. As this increase is

quite impossible, we must conclude either that birds do not rear nearly half their

young, or that the average life of a bird is, from accident, not nearly seven years.

Both checks probably concur. The same kind of calculation applied to all plants

and animals affords results more or less striking, but in very few instances more

striking than in man.

Many practical illustrations of this rapid tendency to increase are on record,

among which, during peculiar seasons, are the extraordinary numbers of certain

animals; for instance, during the years 1826 to 1828, in La Plata, when from

drought some millions of cattle perished, the whole country actually swarmed with

mice. Now I think it cannot be doubted that during the breeding-season all the

mice (with the exception of a few males or females in excess) ordinarily pair, and

therefore that this astounding increase during three years must be attributed to a

greater number than usual surviving the first year, and then breeding, and so on till

the third year, when their numbers were brought down to their usual limits on the

8

Augustine Pyrame de Candolle

Thomas Robert Malthus

return of wet weather. Where man has introduced plants and animals into a new

and favourable country, there are many accounts in how surprisingly few years the

whole country has become stocked with them. This increase would /47-48/ neces-

sarily stop as soon as the country was fully stocked; and yet we have every reason

to believe, from what is known of wild animals, that all would pair in the spring.

In the majority of cases it is most difficult to imagine where the checks fall—

though generally, no doubt, on the seeds, eggs, and young; but when we remem-

ber how impossible, even in mankind (so much better known than any other ani-

mal), it is to infer from repeated casual observations what the average duration of

life is, or to discover the different percentage of deaths to births in different coun-

tries, we ought to feel no surprise at our being unable to discover where the check

falls in any animal or plant. It should always be remembered, that in most cases

the checks are recurrent yearly in a small, regular degree, and in an extreme degree

during unusually cold, hot, dry, or wet years, according to the constitution of the

being in question. Lighten any check in the least degree, and the geometrical pow-

ers of increase in every organism will almost instantly increase the average num-

ber of the favoured species. Nature may be compared to a surface on which rest

ten thousand sharp wedges touching each other and driven inwards by incessant

blows. Fully to realize these views much reflection is requisite. Malthus on man

should be studied; and all such cases as those of the mice in La Plata, of the cattle

and horses when first turned out in South America, of the birds by our calculations

&c., should be well considered. Reflect on the enormous multiplying power inher-ent and annually in action in all animals; reflect on the countless seeds scattered

by a hundred ingenious contrivances, year after year, over the whole face of the

land; and yet we have every reason to suppose that the average percentage of each

of the inhabitants of a country usually remains constant. Finally, let it be borne in

mind that this average number of individuals (the external conditions remaining

the same) in each country is kept up by recurrent struggles against other species or

against external nature (as on the borders of the Arctic regions, where the cold

checks life), and that ordinarily each individual of every species holds its place,

either by its own struggle and capacity of acquiring nourishment in some period of

its life, from the egg upwards; or by the struggle of its parents (in short-lived

organisms, when the main check occurs at longer intervals) with other individuals

of the same or different species.

But let the external conditions of a country alter. If in a small degree, the rela-

tive proportions of the inhabitants will in most cases simply be slightly changed;

but let the number of /48-49/ inhabitants be small, as on an island, and free access

to it from other countries be circumscribed, and let the change of conditions con-

tinue progressing (forming new stations), in such a case the original inhabitants

9

must cease to be as perfectly adapted to the changed conditions as they were orig-

inally. It has been shown in a former part of this work, that such changes of exter-

nal conditions would, from their acting on the reproductive system, probably cause

the organization of those beings which were most affected to become, as under

domestication, plastic. Now, can it be doubted, from the struggle each individual

has to obtain subsistence, that any minute variation in structure, habits, or instincts,

adapting that individual better to the new conditions, would tell upon its vigour

and health? In the struggle it would have a better chance of surviving; and those

of its offspring which inherited the variation, be it ever so slight, would also have

a better chance. Yearly more are bred than can survive; the smallest grain in the

balance, in the long run, must tell on which death shall fall, and which shall sur-

vive. Let this work of selection on the one hand, and death on the other, go on for

a thousand generations, who will pretend to affirm that it would produce no effect,

when we remember what, in a few years, Bakewell effected in cattle, and Western

in sheep, by this identical principle of selection?

To give an imaginary example from changes in progress on an island:— let the

organization of a canine animal which preyed chiefly on rabbits, but sometimes on

hares, become slightly plastic; let these same changes cause the number of rabbits

very slowly to decrease, and the number of hares to increase; the effect of this

would be that the fox or dog would be driven to try to catch more hares: his organ-

ization, however, being slightly plastic, those individuals with the lightest forms,

longest limbs, and best eyesight, let the difference be ever so small, would be

slightly favoured, and would tend to live longer, and to survive during that time of

the year when food was scarcest; they would also rear more young, which would

tend to inherit these slight peculiarities. The less fleet ones would be rigidly

destroyed. I can see no more reason to doubt that these causes in a thousand gen-

erations would produce a marked effect, and adapt the form of the fox or dog to

the catching of hares instead of rabbits, than that greyhounds can be improved by

selection and careful breeding. So would it be with plants under similar circum-

stances. If the number of individuals of a species with plumed seeds could be

increased by greater powers of dissemination within its own area /49-50/ (that is,

if the check to increase fell chiefly on the seeds), those seeds which were provid-

ed with ever so little more down, would in the long run be most disseminated;

hence a greater number of seeds thus formed would germinate, and would tend to

produce plants inheriting the slightly better-adapted down*.

Besides this natural means of selection, by which those individuals are pre-

served, whether in their egg, or larval, or mature state, which are best adapted to

the place they fill in nature, there is a second agency at work in most unisexual

10

*

I can see no more difficulty in this, than in the planter improving his varieties of the cotton plant.—C.D. 1858.

animals, tending to produce the same effect, namely, the struggle of the males for

the females. These struggles are generally decided by the law of battle, but in the

case of birds, apparently, by the charms of their song, by their beauty or their

power of courtship, as in the dancing rock-thrush of Guiana. The most vigorous

and healthy males, implying perfect adaptation, must generally gain the victory in

their contests. This kind of selection, however, is less rigorous than the other; it

does not require the death of the less successful, but gives them fewer descendants.

The struggle falls, moreover, at a time of year when food is generally abundant,

and perhaps the effect chiefly produced would be the modification of the second-

ary sexual characters, which are not related to the power of obtaining food, or to

defence from enemies, but to fighting with or rivalling other males. The result of

this struggle amongst the males may be compared in some respects to that pro-

duced by those agriculturalists who pay less attention to the careful selection of all

their young animals, and more to the occasional use of a choice mate.

II. Abstract of a Letter from C. DARWIN, Esq., to Prof. ASA GRAY, Boston, U.S.,dated Down, September 5th, 1857.

1. It is wonderful what the principle of selection by man, that is the picking out

of individuals with any desired quality, and breeding from them, and again pick-

ing out, can do. Even breeders have been astounded at their own results. They can

act on differences inappreciable to an uneducated eye. Selection has been method-ically followed in Europe for only the last half century; but it was occasionally,

and even in some degree methodically, followed in the most ancient times. There

must have been also a kind of unconscious selection from a remote period, name-

ly in /50-51/ the preservation of the individual animals (without any thought of

their offspring) most useful to each race of man in his particular circumstances.

The “roguing,” as nurserymen call the destroying of varieties which depart from

their type, is a kind of selection. I am convinced that intentional and occasional

selection has been the main agent in the production of our domestic races; but

however this may be, its great power of modification has been indisputably shown

in later times. Selection acts only by the accumulation of slight or greater varia-

tions, caused by external conditions, or by the mere fact that in generation the child

is not absolutely similar to its parent. Man, by this power of accumulating varia-

tions, adapts living beings to his wants — may be said to make the wool of one

sheep good for carpets, of another for cloth, &c.

2. Now suppose there were a being who did not judge by mere external appear-

ances, but who could study the whole internal organization, who was never capri-

cious, and should go on selecting for one object during millions of generations;

11

who will say what he might not effect? In nature we have some slight variation

occasionally in all parts; and I think it can be shown that changed conditions of

existence is the main cause of the child not exactly resembling its parents; and in

nature geology shows us what changes have taken place, and are taking place. We

have almost unlimited time; no one but a practical geologist can fully appreciate

this. Think of the Glacial period, during the whole of which the same species at

least of shells have existed; there must have been during this period millions on

millions of generations.

3. I think it can be shown that there is such an unerring power at work in

Natural Selection (the title of my book), which selects exclusively for the good of

each organic being. The elder De Candolle, W. Herbert, and Lyell have written

excellently on the struggle for life; but even they have not written strongly enough.

Reflect that every being (even the elephant) breeds at such a rate, that in a few

years, or at most a few centuries, the surface of the earth would not hold the prog-

eny of one pair. I have found it hard constantly to bear in mind that the increase of

every single species is checked during some part of its life, or during some short-

ly recurrent generation. Only a few of those annually born can live to propagate

their kind. What a trifling difference must often determine which shall survive, and

which perish!

4. Now take the case of a country undergoing some change. This will tend to

cause some of its inhabitants to vary slightly — /51-52/ not but that I believe most

beings vary at all times enough for selection to act on them. Some of its inhabi-

tants will be exterminated; and the remainder will be exposed to the mutual action

of a different set of inhabitants, which I believe to be far more important to the life

of each being than mere climate. Considering the infinitely various methods which

living beings follow to obtain food by struggling with other organisms, to escape

danger at various times of life, to have their eggs or seeds disseminated, &c. &c.,

I cannot doubt that during millions of generations individuals of a species will be

occasionally born with some slight variation, profitable to some part of their econ-

omy. Such individuals will have a better chance of surviving, and of propagating

their new and slightly different structure; and the modification may be slowly

increased by the accumulative action of natural selection to any profitable extent.

The variety thus formed will either coexist with, or, more commonly, will exter-

minate its parent form. An organic being, like the woodpecker or misseltoe, may

thus come to be adapted to a score of contingences [sic] — natural selection accu-

mulating those slight variations in all parts of its structure, which are in any way

useful to it during any part of its life.

5. Multiform difficulties will occur to every one, with respect to this theory.

Many can, I think, be satisfactorily answered. Natura non facit saltum answers

12

some of the most obvious. The slowness of the change, and only a very few indi-

viduals undergoing change at any one time, answers others. The extreme imper-

fection of our geological records answers others.

6. Another principle, which may be called the principle of divergence, plays, I

believe, an important part in the origin of species. The same spot will support more

life if occupied by very diverse forms. We see this in the many generic forms in a

square yard of turf, and in the plants or insects on any little uniform islet, belong-

ing almost invariably to as many genera and families as species. We can under-

stand the meaning of this fact amongst the higher animals, whose habits we under-

stand. We know that it has been experimentally shown that a plot of land will yield

a greater weight if sown with several species and genera of grasses, than if sown

with only two or three species. Now, every organic being, by propagating so rap-

idly, may be said to be striving its utmost to increase in numbers. So it will be with

the offspring of any species after it has become diversified into varieties, or sub-

species, or true species. And it follows, I think, from the foregoing facts, that the

varying offspring of each species will try /52-53/ (only few will succeed) to seize

on as many and as diverse places in the economy of nature as possible. Each new

variety or species, when formed, will generally take the place of, and thus exter-

minate its less well-fitted parent. This I believe to be the origin of the classifica-

tion and affinities of organic beings at all times; for organic beings always seem to

branch and sub-branch like the limbs of a tree from a common trunk, the flourish-

ing and diverging twigs destroying the less vigorous — the dead and lost branch-

es rudely representing extinct genera and families.

This sketch is most imperfect; but in so short a space I cannot make it better.

Your imagination must fill up very wide blanks.

C. DARWIN.

III. On the Tendency of Varieties to depart indefinitely from the Original Type. By

ALFRED RUSSEL WALLACE.

One of the strongest arguments which have been adduced to prove the orig-

inal and permanent distinctness of species is, that varieties produced in a state of

domesticity are more or less unstable, and often have a tendency, if left to them-

selves, to return to the normal form of the parent species; and this instability is

considered to be a distinctive peculiarity of all varieties, even of those occurring

among wild animals in a state of nature, and to constitute a provision for preserv-

ing unchanged the originally created distinct species.

In the absence or scarcity of facts and observations as to varieties occurring

among wild animals, this argument has had great weight with naturalists, and has

led to a very general and somewhat prejudiced belief in the stability of species.

13

Equally general, however, is the belief in what are called “permanent or true vari-

eties,”—races of animals which continually propagate their like, but which differ

so slightly (although constantly) from some other race, that the one is considered

to be a variety of the other. Which is the variety and which is the original species,

there is generally no means of determining, except in those rare cases in which the

one race has been known to produce an offspring unlike itself and resembling the

other. This, however, would seem quite incompatible with the “permanent invari-

ability of species,” but the difficulty is overcome by assuming that such varieties

have strict limits, and can never again vary further from the original type, although

they may return to it, which, from the /53-54/ analogy of domesticated animals, is

considered to be highly probable, if not certainly proved.

It will be observed that this argument rests entirely on the assumption, that

varieties occurring in a state of nature are in all respects analogous to or even iden-

tical with those of domestic animals, and are governed by the same laws as regards

their permanence or further variation. But it is the object of the present paper to

show that this assumption is altogether false, that there is a general principle in

nature which will cause many varieties to survive the parent species, and to give

rise to successive variations departing further and further from the original type,

and which also produces, in domesticated animals, the tendency of varieties to

return to the parent form.

The life of wild animals is a struggle for existence. The full exertion of all their

faculties and all their energies is required to preserve their own existence and pro-

vide for that of their infant offspring. The possibility of procuring food during the

least favourable seasons, and of escaping the attacks of their most dangerous ene-

mies, are the primary conditions which determine the existence both of individu-

als and of entire species. These conditions will also determine the population of a

species; and by a careful consideration of all the circumstances we may be enabled

to comprehend, and in some degree to explain, what at first sight seems inexplica-

ble — the excessive abundance of some species, while others closely allied to

them are very rare.

The general proportion that must obtain between certain groups of animals is

readily seen. Large animals cannot be so abundant as small ones; the carnivora

must be less numerous than the herbivora; eagles and lions can never be so plen-

tiful as pigeons and antelopes; the wild asses of the Tartarian deserts cannot equal

in numbers the horses of the more luxuriant prairies and pampas of America. The

greater or less fecundity of an animal is often considered to be one of the chief

causes of its abundance or scarcity; but a consideration of the facts will show us

that it really has little or nothing to do with the matter. Even the least prolific of

animals would increase rapidly if unchecked, whereas it is evident that the animal

14

population of the globe must be stationary, or perhaps, through the influence of

man, decreasing. Fluctuations there may be; but permanent increase, except in

restricted localities, is almost impossible. For example, our own observation must

convince us that birds do not go on increasing every year in a geometrical ratio, as

they would do, where there not /54-55/ some powerful check to their natural

increase. Very few birds produce less than two young ones each year, while many

have six, eight, or ten; four will certainly be below the average; and if we suppose

that each pair produce young only four times in their life, that will also be below

the average, supposing them not to die either by violence or want of food. Yet at

this rate how tremendous would be the increase in a few years from a single pair!

A simple calculation will show that in fifteen years each pair of birds would have

increased to nearly ten millions! whereas we have no reason to believe that the

number of the birds of any country increases at all in fifteen or in one hundred and

fifty years. With such powers of increase the population must have reached its lim-

its, and have become stationary, in a very few years after the origin of each species.

It is evident, therefore, that each year an immense number of birds must perish —

as many in fact as are born; and as on the lowest calculation the progeny are each

year twice as numerous as their parents, it follows that, whatever the average num-

ber of individuals existing in any given country, twice that number must perishannually,— a striking result, but one which seems at least highly probable, and is

perhaps under rather than over the truth. It would therefore appear that, as far as

the continuance of the species and the keeping up the average number of individ-

uals are concerned, large broods are superfluous. On the average all above onebecome food for hawks and kites, wild cats and weasels, or perish of cold and

hunger as winter comes on. This is strikingly proved by the case of particular

species; for we find that their abundance in individuals bears no relation whatev-

er to their fertility in producing offspring. Perhaps the most remarkable instance of

an immense bird population is that of the passenger pigeon of the United States,

which lays only one, or at most two eggs, and is said to rear generally but one

young one. Why is this bird so extraordinarily abundant, while others producing

two or three times as many young are much less plentiful? The explanation is not

difficult. The food most congenial to this species, and on which it thrives best, is

abundantly distributed over a very extensive region, offering such differences of

soil and climate, that in one part or another of the area the supply never fails. The

bird is capable of a very rapid and long-continued flight, so that it can pass with-

out fatigue over the whole of the district it inhabits, and as soon as the supply of

food begins to fail in one place is able to discover a fresh feeding-ground. This

example strikingly shows us that the procuring a constant supply /55-56/ of whole-

some food is almost the sole condition requisite for ensuring the rapid increase of

15

a given species, since neither the limited fecundity, nor the unrestrained attacks of

birds of prey and of man are here sufficient to check it. In no other birds are these

peculiar circumstances so strikingly combined. Either their food is more liable to

failure, or they have not sufficient power of wing to search for it over an extensive

area, or during some season of the year it becomes very scarce, and less whole-

some substitutes have to be found; and thus, though more fertile in offspring, they

can never increase beyond the supply of food in the least favourable seasons.

Many birds can only exist by migrating, when their food becomes scarce, to

regions possessing a milder, or at least a different climate, though, as these migrat-

ing birds are seldom excessively abundant, it is evident that the countries they visit

are still deficient in a constant and abundant supply of wholesome food. Those

whose organization does not permit them to migrate when their food becomes

periodically scarce, can never attain a large population. This is probably the rea-

son why woodpeckers are scarce with us, while in the tropics they are among the

most abundant of solitary birds. Thus the house sparrow is more abundant than the

redbreast, because its food is more constant and plentiful,— seeds of grasses being

preserved during the winter, and our farm-yards and stubble-fields furnishing an

almost inexhaustible supply. Why, as a general rule, are aquatic, and especially sea

birds, very numerous in individuals? Not because they are more prolific than the

others, generally the contrary; but because their food never fails, the sea-shores

and river-banks daily swarming with a fresh supply of small mollusca and crus-

tacea. Exactly the same laws will apply to mammals. Wild cats are prolific and

have few enemies; why then are they never as abundant as rabbits? The only intel-

ligible answer is, that their supply of food is more precarious. It appears evident,

therefore, that so long as a country remains physically unchanged, the numbers of

its animal population cannot materially increase. If one species does so, some oth-

ers requiring the same kind of food must diminish in proportion. The numbers that

die annually must be immense; and as the individual existence of each animal

depends upon itself, those that die must be the weakest — the very young, the

aged, and the diseased, — while those that prolong their existence can only be the

most perfect in health and vigour — those who are best able to obtain food regu-

larly, and avoid their numerous enemies. It is, as we commenced by remarking, “a

struggle for existence,” in /56-57/ which the weakest and least perfectly organized

must always succumb.

Now it is clear that what takes place among the individuals of a species must

also occur among the several allied species of a group, — viz. that those which are

best adapted to obtain a regular supply of food, and to defend themselves against

the attacks of their enemies and the vicissitudes of the seasons, must necessarily

obtain and preserve a superiority in population; while those species which from

16

some defect of power or organization are the least capable of counteracting the

vicissitudes of food, [sic] supply, &c., must diminish in numbers, and, in extreme

cases, become altogether extinct. Between these extremes the species will present

various degrees of capacity for ensuring the means of preserving life; and it is thus

we account for the abundance or rarity of species. Our ignorance will generally

prevent us from accurately tracing the effects to their causes; but could we become

perfectly acquainted with the organization and habits of the various species of ani-

mals, and could we measure the capacity of each for performing the different acts

necessary to its safety and existence under all the varying circumstances by which

it is surrounded, we might be able even to calculate the proportionate abundance

of individuals which is the necessary result.

If now we have succeeded in establishing these two points — 1st, that the ani-mal population of a country is generally stationary, being kept down by a period-ical deficiency of food, and other checks; and, 2nd, that the comparative abun-dance or scarcity of the individuals of the several species is entirely due to theirorganization and resulting habits, which, rendering it more difficult to procure aregular supply of food and to provide for their personal safety in some cases thanin others, can only be balanced by a difference in the population which have toexist in a given area — we shall be in a condition to proceed to the consideration

of varieties, to which the preceding remarks have a direct and very important

application.

Most or perhaps all the variations from the typical form of a species must have

some definite effect, however slight, on the habits or capacities of the individuals.

Even a change of colour might, by rendering them more or less distinguishable,

affect their safety; a greater or less development of hair might modify their habits.

More important changes, such as an increase in the power or dimensions of the

limbs or any of the external organs, would more or less affect their mode of

procuring food or the range /57-58/ of country which they inhabit. It is also evi-

dent that most changes would affect, either favourably or adversely, the powers of

prolonging existence. An antelope with shorter or weaker legs must necessarily

suffer more from the attacks of the feline carnivora; the passenger pigeon with less

powerful wings would sooner or later be affected in its powers of procuring a reg-

ular supply of food; and in both cases the result must necessarily be a diminution

of the population of the modified species. If, on the other hand, any species should

produce a variety having slightly increased powers of preserving existence, that

variety must inevitably in time acquire a superiority in numbers. These results

must follow as surely as old age, intemperance, or scarcity of food produce an

increased mortality. In both cases there may be many individual exceptions; but on

the average the rule will invariably be found to hold good. All varieties will there-

17

fore fall into two classes — those which under the same conditions would never

reach the population of the parent species, and those which would in time obtain

and keep a numerical superiority. Now, let some alteration of physical conditions

occur in the district — a long period of drought, a destruction of vegetation by

locusts, the irruption of some new carnivorous animal seeking “pastures new” —

any change in fact tending to render existence more difficult to the species in ques-

tion, and tasking its utmost powers to avoid complete extermination; it is evident

that, of all the individuals composing the species, those forming the least numer-

ous and most feebly organized variety would suffer first, and, were the pressure

severe, must soon become extinct. The same causes continuing in action, the par-

ent species would next suffer, would gradually diminish in numbers, and with a

recurrence of similar unfavourable conditions might also become extinct. The

superior variety would then alone remain, and on a return to favourable circum-

stances would rapidly increase in numbers and occupy the place of the extinct

species and variety.

The variety would now have replaced the species, of which it would be a more

perfectly developed and more highly organized form. It would be in all respects

better adapted to secure its safety, and to prolong its individual existence and that

of the race. Such a variety could not return to the original form; for that form is an

inferior one, and could never compete with it for existence. Granted, therefore, a

“tendency” to reproduce the original type of the species, still the variety must ever

remain preponderant in numbers, and under adverse physical conditions againalone survive. /58-59/ But this new, improved, and populous race might itself, in

course of time, give rise to new varieties, exhibiting several diverging modifica-

tions of form, any of which, tending to increase the facilities for preserving exis-

tence, must, by the same general law, in their turn become predominant. Here,

then, we have progression and continued divergence deduced from the general

laws which regulate the existence of animals in a state of nature, and from the

undisputed fact that varieties do frequently occur. It is not, however, contended

that this result would be invariable; a change of physical conditions in the district

might at times materially modify it, rendering the race which had been the most

capable of supporting existence under the former conditions now the least so, and

even causing the extinction of the newer and, for a time, superior race, while the

old or parent species and its first inferior varieties continue to flourish. Variations

in unimportant parts might also occur, having no perceptible effect on the life-pre-

serving powers; and the varieties so furnished might run a course parallel with the

parent species, either giving rise to further variations or returning to the former

type. All we argue for is, that certain varieties have a tendency to maintain their

existence longer than the original species, and this tendency must make itself felt;

18

for though the doctrine of chances or averages can never be trusted to on a limit-

ed scale, yet, if applied to high numbers, the results come nearer to what theory

demands, and, as we approach to an infinity of examples, become strictly accurate.

Now the scale on which nature works is so vast — the numbers of individuals and

periods of time with which she deals approach so near to infinity, that any cause,

however slight, and however liable to be veiled and counteracted by accidental cir-

cumstances, must in the end produce its full legitimate results.

Let us now turn to domesticated animals, and inquire how varieties produced

among them are affected by the principles here enunciated. The essential differ-

ence in the condition of wild and domestic animals is this, — that among the for-

mer, their well-being and very existence depend upon the full exercise and healthy

condition of all their senses and physical powers, whereas, among the latter, these

are only partially exercised, and in some cases are absolutely unused. A wild ani-

mal has to search, and often to labour, for every mouthful of food—to exercise

sight, hearing, and smell in seeking it, and in avoiding dangers, in procuring shel-

ter from the inclemency of the seasons, and in providing for the subsistence and

safety of its offspring. There is no muscle of /59-60/ its body that is not called into

daily and hourly activity; there is no sense or faculty that is not strengthened by

continual exercise. The domestic animal, on the other hand, has food provided for

it, is sheltered, and often confined, to guard it against the vicissitudes of the sea-

sons, is carefully secured from the attacks of its natural enemies, and seldom even

rears its young without human assistance. Half of its senses and faculties are quite

useless; and the other half are but occasionally called into feeble exercise, while

even its muscular system is only irregularly called into action.

Now when a variety of such an animal occurs, having increased power or

capacity in any organ or sense, such increase is totally useless, is never called into

action, and may even exist without the animal ever becoming aware of it. In the

wild animal, on the contrary, all its faculties and powers being brought into full

action for the necessities of existence, any increase becomes immediately avail-

able, is strengthened by exercise, and must even slightly modify the food, the

habits, and the whole economy of the race. It creates as it were a new animal, one

of superior powers, and which will necessarily increase in numbers and outlive

those inferior to it.

Again, in the domesticated animal all variations have an equal chance of con-

tinuance; and those which would decidedly render a wild animal unable to com-

pete with its fellows and continue its existence are no disadvantage whatever in a

state of domesticity. Our quickly fattening pigs, short-legged sheep, pouter

pigeons, and poodle dogs could never have come into existence in a state of nature,

because the very first step towards such inferior forms would have led to the rapid

19

extinction of the race; still less could they now exist in competition with their wild

allies. The great speed but slight endurance of the race horse, the unwieldy

strength of the ploughman’s team, would both be useless in a state of nature. If

turned wild on the pampas, such animals would probably soon become extinct, or

under favourable circumstances might each lose those extreme qualities which

would never be called into action, and in a few generations would revert to a com-

mon type, which must be that in which the various powers and faculties are so pro-

portioned to each other as to be best adapted to produce food and secure safety, —

that in which by the full exercise of every part of his organization the animal can

alone continue to live. Domestic varieties, when turned wild, must return to some-

thing near the type of the original stock, or become altogether extinct. /60-61/

We see, then, that no inferences as to varieties in a state of nature can be

deduced from the observation of those occurring among domesticated animals.

The two are so much opposed to each other in every circumstance of their exis-

tence, that what applies to the one is almost sure not to apply to the other.

Domestic animals are abnormal, irregular, artificial; they are subject to varieties

which never occur and never can occur in a state of nature: their very existence

depends altogether on human care; so far are many of them removed from that just

proportion of faculties, that true balance of organization, by means of which alone

an animal left to its own resources can preserve its existence and continue its race.

The hypothesis of Lamarck — that progressive changes in species have been

produced by the attempts of animals to increase the

development of their own organs, and thus modify

their structure and habits — has been repeatedly and

easily refuted by all writers on the subject of varieties

and species, and it seems to have been considered

that when this was done the whole question has been

finally settled; but the view here developed renders

such an hypothesis quite unnecessary, by showing

that similar results must be produced by the action of

principles constantly at work in nature. The powerful

retractile talons of the falcon- and cat-tribes have not

been produced or increased by the volition of those

animals; but among the different varieties which occurred in the earlier and less

highly organized forms of these groups, those always survived longest which hadthe greatest facilities for seizing their prey. Neither did the giraffe acquire its long

neck by desiring to reach the foliage of the more lofty shrubs, and constantly

stretching its neck for the purpose, but because any varieties which occurred

among its antitypes with a longer neck than usual at once secured a fresh range of

20

Jean-Baptiste Lamarck

pasture over the same ground as their shorter-necked companions, and on the firstscarcity of food were thereby enabled to outlive them. Even the peculiar colours of

many animals, especially insects, so closely resembling the soil or the leaves or the

trunks on which they habitually reside, are explained on the same principle; for

though in the course of ages varieties of many tints may have occurred, yet thoseraces having colours best adapted to concealment from their enemies wouldinevitably survive the longest. We have also here an acting cause to account for

that balance so often observed in nature, — a deficiency in one set of organs

always being compensated by an increased development of some others — pow-

erful wings accompanying weak /61-62/ feet, or great velocity making up for the

absence of defensive weapons; for it has been shown that all varieties in which an

unbalanced deficiency occurred could not long continue their existence. The

action of this principle is exactly like that of the centrifugal governor of the steam

engine, which checks and corrects any irregularities almost before they become

evident; and in like manner no unbalanced deficiency in the animal kingdom can

ever reach any conspicuous magnitude, because it would make itself felt at the

very first step, by rendering existence difficult and extinction almost sure soon to

follow. An origin such as is here advocated will also agree with the peculiar char-

acter of the modifications of form and structure which obtain in organized beings

— the many lines of divergence from a central type, the increasing efficiency and

power of a particular organ through a succession of allied species, and the remark-

able persistence of unimportant parts, such as colour, texture of plumage and hair,

form of horns or crests, through a series of species differing considerably in more

essential characters. It also furnishes us with a reason for that “more specialized

structure” which Professor Owen states to be a characteristic of recent compared

with extinct forms, and which would evidently be the result of the progressive

modification of any organ applied to a special purpose in the animal economy.

We believe we have now shown that there is a tendency in nature to the con-

tinued progression of certain classes of varieties further and further from the orig-

inal type — a progression to which there appears no reason to assign any definite

limits — and that the same principle which produces this result in a state of nature

will also explain why domestic varieties have a tendency to revert to the original

type. This progression, by minute steps, in various directions, but always checked

and balanced by the necessary conditions, subject to which alone existence can be

preserved, may, it is believed, be followed out so as to agree with all the phenom-

ena presented by organized beings, their extinction and succession in past ages,

and all the extraordinary modifications of form, instinct, and habits which they

exhibit.

Ternate, February, 1858

21

COMMENTARY

Charles Darwin was born at Shrewsbury on February 12, 1809. His father was

a wealthy physician and his mother was the daughter of a manufacturer, Josiah

Wedgwood. He, therefore, had independent means, which allowed him to pursue

his scientific interests without having to earn a living. After a couple of years of

medical school, he went to Cambridge University to prepare for a career as a cler-

gyman. He had, however, developed a taste for the natural sciences and became

the unofficial naturalist on a surveying expedition that took him around the world

(1831-1836). During the voyage he read Charles Lyell’s Principles of Geology,

and he made some important discoveries about geology. As a result, he became

both a protégé of Lyell, and one of his main supporters. He also studied the min-

erals, plants and animals, and collected a vast quantity of natural history speci-

mens. As a consequence, he made many observations on the geographical distri-

bution of organisms, especially those of islands.

After he returned to England Darwin realized that the geographical distribution

of animals and the relationships some of the fossils that he found in South America

to living animals were evidence for evolution. He began to search for a mechanism

that could account for it, speculating as he read about a wide range of topics. In

late September of 1838, he read a book on political economy, [Thomas] Robert

Malthus’ An Essay on the Principle of Population. Malthus argued that human

populations grow rapidly as long as food is abundant. Although the food supply

can be increased, that increase is not sufficient to maintain a high level of popula-

tion growth indefinitely. Ultimately food will become scarce, standards of living

will fall, and population numbers will stabilize. He said that population increases

geometrically, whereas resources are augmented arithmetically. The mathematics

was not a crucial part of Malthus’s argument. Malthus and others had noted that

when population numbers are decreased owing to a plague, there follows a period

in which people bear and raise more offspring so that the population tends to return

to its former levels and stabilize. Likewise, when new land is opened up to culti-

vation, as in North America, the abundant food supply leads to a higher reproduc-

tive rate. Darwin realized that any advantage that an individual organism might

have in avoiding enemies and utilizing the available resources relative to other

organisms of the same species would mean that it would leave relatively more off-

spring. Whatever properties that gave the organism that advantage would tend to

be passed on to the next generation, transforming the species. Evolution would

result from reproductive competition between organisms of the same species.

Darwin already was well aware of the fact that breeders of domesticated animals

and plants were able to effect changes by “selecting” the organisms with the

desired traits and using them as breeding stock. He now understood that something

22

similar to what happens under artificial conditions would result because of the

scarcity of resources under natural conditions. The environment would take the

place of the breeder. Darwin now had a plausible mechanism for evolution, and

one that was similar to a familiar process.

Darwin speculated a great deal and gradually elaborated the theory of evolu-

tion by natural selection that was published in The Origin of Species. But twenty

years elapsed between that event and his reading of Malthus. Various reasons have

been given for the delay. The most obvious and straight forward is that he needed

to publish the results of his geological research. His work was much delayed by

illness, no doubt exacerbated by anxiety. In retrospect we can find many hints of

Darwin’s evolutionism in his earlier publications. Among these was his semi-pop-

ular account of his travels, a book which has appeared under various titles, the

most appropriate of which is the Journal of Researches. It appeared in two edi-

tions. The first, published in 1839, was written when Darwin was already an evo-

lutionist, but before he had read Malthus. The second was prepared in 1845 and

contains a great deal of material that is relevant to Darwin’s ideas about natural

selection and the competitive natural economy. It even includes a discussion of the

Malthusian notion of geometrical population increase. Prior to that time, however,

Darwin had begun to prepare a book on his theory. A “Sketch” of this theory was

produced in 1842. This was basically a working outline with notes and memoran-

da. A much longer “Essay” was completed in 1844. It is from this manuscript that

the excerpt in the Darwin-Wallace paper was taken. Darwin realized that it would

take a considerable amount of time and work to get the manuscript into a form in

which it could be published. He feared that he might die before completing it.

Therefore he made arrangement for its posthumous publication. Having become a

good friend of the botanist Joseph Hooker, Darwin thought he might be a suitable

editor, and in 1847 he sent Hooker a copy.

In 1848, Darwin began to do some zoological work. The result was that he

wrote a monograph on barnacles well over a thousand pages long. That delayed

serious work on his book on evolution until around September of 1854. Although

only implicitly so, the barnacle monograph was in fact Darwin’s first book on evo-

lution. It made him a very eminent zoologist who could speak with authority on a

vast range of biological matters and he found the research very instructive. One

discovery that he made while doing the barnacle research was what he called “the

principle of divergence of character.” As he saw it, the various groups in the natu-

ral system of classification are lineages connected by common ancestry. They

become increasingly diversified with the passage of time because it is advanta-

geous for the organisms to seize upon different places in the economy of nature,

or, as we would now say, to occupy a variety of niches. This notion was basic to

23

Darwin’s evolutionary ecology. Darwin began to organize his notes on evolution-

ary topics and did a considerable amount of experimental and comparative

research.

Meanwhile Alfred Russel Wallace was thinking along somewhat similar lines.

Born in 1828, Wallace came from a family of very modest means. Largely self-

educated, he early on became an amateur naturalist. In his readings he encountered

some of the pre-Darwinian evolutionary, or proto-evolutionary, literature. The

topic was not considered intellectually respectable at the time. Indeed it was con-

sidered socially and politically reprehensible. Wallace, who had very much a mind

of his own, was favorably disposed to it nonetheless. Around the time that the sec-

ond edition of Darwin’s Journal of Researches was published, which Wallace read,

he also read Malthus’ essay on population. It seems likely that Wallace gained

some hints about Darwin’s views from his readings.

Wallace became the friend of another amateur naturalist who later became a

famous evolutionist, Henry Walter Bates. Together they decided to undertake an

expedition to the Amazon in the hope of finding evidence that might bear upon the

larger evolutionary questions. Their plan was to collect natural history specimens

and sell some of them to dealers as a means of financing the expedition. In this

they were successful, but some of Wallace’s collections were destroyed by a fire

at sea on the way back to England in 1852.

Undaunted, Wallace embarked upon a similar

research and collecting trip to the Malay

Archipelago, reaching Singapore in April, 1854. In

spite of great hardship, he explored a vast area and

collected a remarkable number of specimens.

Wallace’s biogeographical studies led him to the

same conclusions that Darwin’s had. In 1855, he pub-

lished a paper entitled “On the law which has regulat-

ed the introduction of new species.” His point was

that whenever a new species appears, it does so close

(both in space and time) to a closely-related and pre-

viously-existing species. The implication would be

that one species has given rise to another.

Wallace’s paper attracted the attention of Lyell as well as Darwin. During a

visit to Darwin’s home in 1856, Lyell asked about Darwin’s theory, and Darwin

explained it. Realizing that Wallace was working along the same lines, Lyell urged

Darwin to publish. So Darwin began to write a long book, to be entitled NaturalSelection, in which he would expound his theory at great length, and in minute

detail. That same year, Darwin began to correspond with the Harvard botanist Asa

24

Henry Walter Bates

Gray, in the hope of obtaining some information about plants that he wanted. In

that letter, Darwin revealed that he was working on evolutionary theory. In May of

1857, Darwin also wrote to Wallace, informing him that he had a species theory.

And, in September (or October), he again wrote to Gray, explaining natural selec-

tion. That letter provided part of the joint publication. In December, Darwin once

more wrote to Wallace, commenting on another of Wallace’s papers. In his letter,

Darwin said that he was working on a book about his theory, but that it would be

some time before it would be ready for publication.

In February 1858, perhaps quite soon after Darwin’s letter had reached him,

Wallace, while suffering from a bout of malaria, discovered natural selection. He

wrote a manuscript explaining the idea and sent it to Darwin with a covering let-

ter asking for his opinion and saying that if he felt that it was of any value to send

it on to Lyell. Darwin had been making slow but steady progress on NaturalSelection and was astonished when Wallace’s manuscript arrived on June 18. He

immediately got in touch with Hooker and Lyell, who arranged for the joint pub-

lication that was read before the Linnaean Society on July 1. Although their cov-

ering letter is dated June 30, the arrangement must have occurred somewhat earli-

er. In effect, everything was set up in about a week’s time. Very little is known

about what actually went on. Darwin himself was not much involved, for he was

at his home in the country, and was distracted by such events as the death of his

youngest child. Darwin was much upset about the whole affair. He went on vaca-

tion for a few weeks, but on July 20 he began to write what he called an “abstract”

of Natural Selection.

Wallace could not have been aware of what was going on at the time, and

Darwin was really worried as to how Wallace would react. Would he feel that he

had been treated unfairly? But, in due course, Wallace was informed of what had

taken place, and on October 6 he wrote a letter to Hooker saying that he approved

of the joint publication.

Meanwhile, Darwin began a new manuscript of a shorter book, still intending

to publish the long one that he had been working on when Wallace’s manuscript

arrived. Although the official date of publication of this “abstract,” The Origin ofSpecies, was November 24, 1859, the entire edition was sold at the publishers’

trade sale on November 22. Some prepublication copies were available somewhat

earlier, and of course Wallace was among the recipients. Wallace was profoundly

impressed. In a letter to Bates dated December 24, 1860 he evaluates the book as

follows:

I do not know how or to whom to express fully my admiration of Darwin’s book. To him

it would seem flattery, to others self-praise; but I do honestly believe that with however

much patience I had worked up and experimented on the subject, I could never have

25

approached the completeness of his book—its vast accumulation of evidence, its over-

whelming argument, and its admirable tone and spirit. I really feel thankful that it has not

been left to me to give the theory to the public. Mr. Darwin has created a new science and

a new philosophy, and I believe that never has such a complete illustration of a new

branch of knowledge been due to the labours and researches of a single man. Never have

such vast masses of widely scattered and hitherto disconnected facts been combined into

a system, and brought to bear upon the establishment of such a grand and new and sim-

ple philosophy!

Wallace returned to London on April 1, 1862, and he and Darwin met soon

after Darwin arrived by train the next day, probably at the home of Darwin’s older

brother, Erasmus Alvey Darwin. Wallace became one of Darwin’s most effective

supporters. Darwin, conversely, went out of the way to give Wallace full credit as

co-discoverer of natural selection. They often disagreed about various topics both

scientific and philosophical, but their discussions were always cordial. Their main

area of disagreement had to do with human evolution. Wallace denied that natural

selection could explain human mentality. With that one exception, however,

Wallace attributed more to natural selection than Darwin did. Wallace was rather

eccentric and openly endorsed spiritualism. That created something of a strain

with Darwin, and more than that with Hooker and some other scientists. Although

he was able to earn money by writing and lecturing, Wallace was never able to

obtain suitable employment. In addition, he was inept at handling his financial

affairs. Darwin arranged for a government pension for him. Wallace was a prolif-

ic contributor to the literature on evolutionary biology. Perhaps his most important

contributions were to biogeography. His Island Life and Geograpical Distributionof Animals are both classics. Darwin had, in effect, opted out of working on bio-

geography and left the topic largely to Wallace.

Since Wallace gracefully went along with the arrangement for joint publi-

cation, the issue of whether Wallace was treated fairly or not is academic. He knew

that Darwin had a theory and had many hints of what it was. The discovery was

not as “independent” of Darwin as one might think. His manuscript was circulat-

ed for comments by Darwin and Lyell and not submitted for publication. If it had

been published separately, it likely would not have attracted much attention any-

how. On the other hand, the joint publication made Wallace a famous man. He was

welcomed into scientific circles. His books and papers, both scholarly and popu-

lar, were much esteemed and widely read. And, quite unwittingly, he got Darwin

to write a much shorter book and a better one, and to present it to the world much

sooner than he had intended.

26

CHRONOLOGY

27

1809

12 February, Charles Darwin born

1823

8 January, Alfred Russel Wallace born

1828

January, Darwin began studies at Cambridge

1831

27 December, Darwin left England on voyage around

the world

1832

28 February, Darwin arrived in South America

1836

2 October, Darwin arrived in England

1837

7-12 March, Darwin became an evolutionist

1838

28 September-2 October, Darwin read Malthus’s

Essay on the Principle of Population and discov-

ered natural selection

1839

1 June, Darwin’s Journal of Researches published

1842 Darwin wrote a “Sketch” of his evolutionary

thory

1844

11 January, Darwin wrote to Joseph Hooker, reveal-

ing his evolutionary views

5 July, Darwin completed his Essay on evolution

1844-1846

Wallace, a school teacher at Leicester, read Malthus’s

Essay on the Principle of Population and

Darwin’s Journal of Researches (probably the

second edition)

1845

5 April, Darwin finished preparation of the second

edition of his Journal of Researches

1847

7 January, Hooker received a copy of Darwin’s 1844

Essay

1848

26 May, Wallace and Bates reached the Amazon

1 October, Darwin began to work on barnacles

1852

12 July, Wallace departed for England, arriving 1

October

1854

20 April, Wallace arrived in Singapore

9 September, having completed his work on barna-

cles, Darwin began to write a book on species

1855

September, Wallace’s paper “On the law which has

regulated the introduction of new species” pub-

lished

1856

13-16 April, during a visit to Darwin, Charles Lyell

asked about Wallace’s paper of 1855; Darwin told

him about natural selection; Lyell urged him to

publish

14 May, Darwin began to work on manuscript of

Natural Selection and continued to do so until

Wallace’s manuscript arrived in 1858

20 July, Darwin, in a letter to Asa Gray, reveals his

evolutionary views

1857

1 May, in a letter to Wallace, in which Darwin com-

ments on Wallace’s 1855 paper, he remarks that

he has a species theory

20 July, Darwin wrote an openly evolutionary letter

to Gray

5 September, Darwin sends a letter to Gray with an

enclosure explaining natural selection

27 September, Wallace responded to Darwin’s letter

of 1 May

29 November, Darwin clarifies his evolutionary ideas

in a letter to Gray

22 December, responding to Wallace’s letter of 27

September, Darwin comments on Wallace’s paper

and says that he has plans for a book

1858

February, Wallace discovered natural selection

18 June, Wallace’s manuscript on natural selection

reached Darwin, who wrote to Lyell

28 June, Darwin’s infant son, Charles Waring

Darwin, died

1 July, the joint paper was read to the Linnaean

Society; it was published in August

6 October, in a letter to Hooker, Wallace expresses

approval of joint publication

ACKNOWLEDGMENTS

I want to take this opportunity to thank Dr. Michele Aldrich, who kindly assist-

ed me in proof reading the text against the original publication and otherwise

offered several suggestions for the improvement of the overall presentation.

REFERENCES

BURKHARDT, FREDERICK ET AL. 1985-continuing. The Correspondence of Charles Darwin (15 vols. to date

covering period 1821–1867). Cambridge University Press, Cambridge, UK. {NB. vol. 7 for year 1858}

DARWIN, CHARLES. 1845. Journal of Researches into the Natural History and Geology of the Countries Visitedduring the Voyage of H.M.S. Beagle round the World, 2

nd

edition. John Murray, London. 519 pp.

DARWIN, CHARLES. 1859. On the Origin of Species by Means of Natural Selection, or the Preservation ofFavoured Races in the Struggle for Life, 1

st

ed. John Murray, London. ix + 502 pp.

DARWIN, CHARLES, AND ALFRED RUSSEL WALLACE. 1858. On the tendency of species to form varieties; and on

the perpetuation of varieties and species by natural means of selection. Journal of the Proceedings of theLinnaean Society (Zoology) 3([20 August]):45–62.

MALTHUS, [THOMAS] ROBERT. 1798. An Essay on the Principle of Population, as it Affects the FutureImprovement of Society, with Remarks on the Speculations of Mr. Godwin, M. Condorcet, and OtherWriters [1

st

ed.]. [Printed for] J. Johnson, London. v + ix + 396 pp.

MARCHANT, JAMES. 1916. Alfred Russel Wallace: Letters and Reminiscences. Harper & Brothers, New York.

viii + 507 pp.

WALLACE, ALFRED RUSSEL. 1855. On the law which has regulated the introduction of new species. Annals andMagazine of Natural History, 2, v. 16, p. 184–196; Published September 1855.

WALLACE, ALFRED RUSSEL. 1876. The Geographical Distribution of Animals: with a Study of the Relations ofLiving and Extinct Faunas as Elucidating the Past Changes of the Earth's Surface. Macmillan, London.

xxiv + 503 + xi + 607 pp.

WALLACE, ALFRED RUSSEL. 1880. Island Life: or, the Phenomena and the Causes of Insular Faunas andFloras, Including a Revision and Attempted Solution of the Problem of Geological Climates [1

st

ed.].

Macmillan, London. vii + 526 pp.

WALLACE, ALFRED RUSSEL. 1905. My Life: a Record of Events and Opinions. Dodd, Mead, New York. ix +

435 + vii + 464 pp.

28

1859

24 November, The Origin of Species published

1860

24 December, Wallace wrote Bates, praising TheOrigin of Species

1862

20 February, Wallace left Singapore, arriving in

London April 1

1882

19 April, Darwin died

1913

7 November, Wallace died

Copyright (c) 2008 by the California Academy of Sciences

San Francisco, California 94118